Even when their bullpen is fully healthy, 34-year-old left-hander Jeremy Affeldt is one of the most trusted relievers in the San Francisco Giants‘ bullpen. He sits atop the lefty totem pole, and he has split setup duties with righty Santiago Casilla for a long time now. However, in Casilla’s absence, Affeldt has been trusted with setup responsibilities versus both left-handed and right-handed hitters, and it hasn’t worked out too well.

It would not be the most ridiculous thing in the world if Giants ace Matt Cain held a grudge against Affeldt, as he has blown two of Cain’s best starts of the season during the past month. On June 7, Affeldt gave up a costly home run to Paul Goldschmidt in the eighth inning and took the loss against the Arizona Diamondbacks, after Cain had given up one run and four hits over seven innings. Then on Saturday versus the Colorado Rockies, Affeldt was trusted with a tie game in the ninth inning, after Cain gave up one run and three hits over eight innings. He once again could not deliver and gave up a walk off hit to Rockies rookie Nolan Arenado.

After a fantastic May in which he had a 0.73 ERA over 14 appearances, Affeldt has taken a huge turn for the worse in June. He has taken three losses and has a 5.23 ERA in 11 games. Affeldt is probably overjoyed by Casilla’s impending return; his splits have been on completely opposite sides of the spectrum, as he has a dominant 0.71 ERA versus lefties, and a 5.52 split against right-handed hitters.

While Affeldt can be pushed back into more of a specialist role with the return of Casilla, really he has done enough to lose the constant trust that he’s been given in crucial situations. Though he deserves some leeway because of his previous performance and his $6 million yearly salary, he has been outperformed by his fellow lefty Jose Mijares this year. Over one extra third of an inning, Mijares has a 2.60 ERA compared to Affeldt’s 3.29. Mijares is better suited to the setup role, as he has a 2.13/3.00 lefty/righty ERA split. And he has 26 strikeouts compared to Affeldt’s 17.

Though Affeldt should not be given up on and should be a key part of this bullpen for years to come, perhaps it is time to give Mijares a chance in the setup role. The 28-year-old has not been put in very many crucial situations, and this kind of change may be the type of move that can help the Giants work out of the awful slump they’ve been in recently. It could allow Affeldt to regain his confidence in some low-risk situations and make him available for more lefty specialist chances, in which he is proven to be fully effective. Though he’s probably not the player who most deserves to be made an example of, change often sparks results, and this is the kind of move that could boost the Giants.

Patrick Karraker is a San Francisco Giants writer for RantSports.com. Follow him on Twitter @PatrickKarraker, “Like” him on Facebook, or add him to your network on Google+.

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